如何使用ctypes-python指针更改结构字段

Question

下面是我使用ctypes访问dll值的代码。

我的意图是存储结构字段地址。每当结构中的值发生变化时，我就可以访问地址并获得更改后的值。

DUMMY_DLL_PATH = "dummyModel.dll"
class MyStruct(ctypes.Structure):  
    _fields_ = [("field_one", ctypes.c_int),  
                ("field_two", ctypes.c_int)]  
d_m = ctypes.cdll.LoadLibrary(DUMMY_DLL_PATH)  
d_i = MyStruct.in_dll(d_m,"dummy_In")  
in_field = ctypes.c_int(d_i.field_one)  
#storing the address  
b = ctypes.addressof(in_field)  
b_v = ctypes.cast(b,ctypes.POINTER(ctypes.c_int))  
k= b_v.contents   
print 'before',d_i.field_one,k.value  
#changing the value  
d_i.field_one = 10  
print 'After',d_i.field_one,k.value  

输出：

Before 0 0  
After 10 0  

通过指针，值不会更改。保持0

Answer 1

问题是in_field是一个新的c_int对象，占用的内存与原始结构不同。您想要的是c_int.from_buffer（docs），它共享原始对象的内存。这里有一个例子：

使用cl /LD x.c编译的Windows DLL源x.c：

struct MyStruct
{
    int one;
    int two;
};
__declspec(dllexport) struct MyStruct myStruct = {1,2};

Python脚本：

from ctypes import *
class MyStruct(Structure):
    _fields_ = [
        ("one", c_int),
        ("two", c_int)]
    def __repr__(self):
        return 'MyStruct({},{})'.format(self.one,self.two)
dll = CDLL('x')
struct = MyStruct.in_dll(dll,"myStruct")
alias1 = c_int.from_buffer(struct, MyStruct.one.offset)
alias2 = c_int.from_buffer(struct, MyStruct.two.offset)
print struct
print 'before',alias1,alias2
struct.one = 10
struct.two = 20
print 'after',alias1,alias2

输出：

MyStruct(1,2)
before c_long(1) c_long(2)
after c_long(10) c_long(20)